1. Field of the Invention
The invention relates to a method of operating a synchronous motor having a stator comprising a set of electromagnets and having a permanent magnet rotor. Such a motor is often called permanent magnet synchronous motor (PMSM). The invention further relates to an arrangement for operating such a motor. A particular field of interest is the control of a PMSM which is a propulsion motor of a rail vehicle.
2. Description of Related Art
Typically, asynchronous motors having a rotor with at least one electromagnet are used for propulsion of rail vehicles. The term “rail vehicles” includes any track-bound vehicle. These asynchronous motors can easily be controlled, since not only the electromagnets of the stator, but also the electromagnet or electromagnets of the rotor can be adapted to the desired operational behaviour. However, PMSM motors have some advantages. Especially, the power density (the achievable power per volume) is high and the energy losses are low. On the other hand, as mentioned, the control of a PMSM is more difficult, if a fast response of the motor is required in dynamic situations and if efficient use of resources (in particular available electric voltage and energy) is of importance.
Usually, there are limits for the operation parameters of the motor. Some of the limits may depend on the operation state, some of the limits are fixed for the motor. In particular, these limits are: a maximum value of the stator flux allowed for the motor, the value of the electric voltage which is used to drive the currents through the stator electromagnets, a maximum value for these currents which is allowed and the maximum allowed torque which is allowed for the motor.